A conventional strain detector is disclosed in, for example, Japanese Patent Unexamined Publication No. H8-87375. FIG. 12 is a bottom view showing a conventional strain detector, FIG. 13 is a perspective view showing the strain detector, and FIG. 14 is a cross sectional view showing a state, in which the strain detector is mounted.
Insulating substrate (hereinafter referred to as substrate) 1 includes an elastic member and an insulating layer formed on the surface thereof. Insulating substrate 1 is fixed to a lower surface of push member 2. Four strain resistance elements (hereinafter referred to as elements) 3 are provided on a lower surface of insulating substrate 1. Four strain resistance elements 3 are electrically connected to a pair of source electrodes 4, a pair of output electrodes 5, and a pair of earthed electrodes 6. Thereby, a bridge circuit is constituted.
An operation of the conventional strain detector constructed as described above is discussed hereinafter. As shown in FIG. 14, the strain detector is fixed to fixed member 7 by screws 8 in use. When a push force is applied to an upper surface substantially centrally of insulating substrate 1 through push member 2, the push force generates a bending moment on insulating substrate 1. The bending moment generates a bending moment also on four elements 3 provided on the lower surface of insulating substrate 1. When the bending moment is generated on elements 3, elements 3 are varied in value of resistance. Such variation in value of resistance is output from pair of output electrodes 5 to an external computer (not shown), and a push force applied to substrate 1 is calculated.
In the conventional construction mentioned above, substrate 1 is clamped and fixed to fixed member 7 by screws 8. Therefore, a fixed position is displaced when a shock is applied, so that a fixed length constructed as a beam is varied and the strain detector is degraded in characteristics such as sensitivity and 0-point voltage.